1. Field of the Invention
The present invention relates to positive displacement machines for incompressible media.
2. Discussion of Related Art
Positive displacement machines with circular displacement bodies for liquids have been known since 1905, as disclosed in DE 177 654. However, such a machine was an annular piston extending into the conveying chamber in an oscillating manner, for which it is guided on the land separating the inlet from the outlet. It is driven by a crank on which it is mounted by means of a hub. This machine is characterized allegedly by an uninterrupted and uniform discharge.
Another displacement machine, not with circular but with heart shaped displacement vanes, is disclosed in WO 86/05241. In this pump displacement, vanes are moved simultaneously in a cyclic motion relative to their chambers by means of a crank drive. A radially adjustable element produces a driving force with radial and tangential components acting on the support of the displacement vanes, so that the latter always remain in a sealing contact with their chambers. The adjustable element may act in the manner of a spring, a wedge, or by any other frictional but not positive means. The support carrying the displacement vanes does not tilt in any position because of the opposing contact locations of the vanes arranged in a ring.
Similar displacement machines with a wobble drive are disclosed in DE 2 603 462 and U.S. Pat. No. 3,560,119. Other machines of this type with an Oldham coupling are also disclosed in EP 10930 B1, U.S. Pat. No. 4,437,820 and DE 27 35 664. All of these installations are so-called displacement machines for compressible media. They each comprise a working chamber defined by helical circumferential walls extending vertically from a side wall and leading from an inlet located outside the helices to an outlet inside the helices. They further contain a helical displacement body extending into the working chamber. The latter is supported rotatingly without rotation relative to the working chamber. Its center is eccentrically offset relative to the center of the circumferential walls, so that the displacement body is always in contact with both the outer and the inner circumferential wall of the working chamber along at least one advancing line. During the operation of the machine therefore a plurality of sickle shaped working spaces are enclosed. The working spaces move from the inlet to the outlet through the working chamber. Depending on the angle of contact of the helix, the volume of the working medium conveyed may be gradually reduced with a corresponding increase of the pressure of said medium.
In those known machines, the tumble drive is always the means to convert the rotating motion of the driving machine into the translatory motion of the displacer.
The drive solution in DE 2,603,462 consists of an eccentric body mounted with a counter weight on the drive shaft, upon which a drive disk is located by means of a ball bearing. The latter is equipped with four ball jointed sockets in which the ball end of the wobble rod is located. The balls there are only in line contact with their sockets. During a rotating motion of the drive shaft, the rotor body is placed into a circling but not rotating motion by the wobble rods. In addition to the driving function, in this solution the wobble rods also secure the body against rotation.
In the configuration according to U.S. Pat. No. 3,560,119, the pivot of the wobble rod on the drive side is supported rotatingly and pivotingly in an eccentric position by means of a pendulum ball bearing. To prevent the rotation of the displacer itself, the second and third ball sections are provided with sectional crowns, for example, teeth, which engage the correspondingly profiled counter pieces in the displacer and the stationary housing part and are pivotingly supported in them. The wobble shaft is axially secured by means of a retaining disk fitting into the stationary housing part.
In the known machines, the relative rotating motion is always transmitted by a highly stressed and thus expensive ball bearing. Furthermore, no measure is provided to insure the operation without clearance of the machine in case of the wear of the material of the wobble rod or rods. In all of those known machines, Oldham (cross-keyed) couplings are the rotation inhibiting means for the displacer. Radial displacement is limited by the contact of the helical ribs with the walls of the working chambers. This limitation theoretically corresponds to a circle, in this case a translational circle. The displacer, which is not rotating relative to the working chamber, must be guided by means of the Oldham coupling in a manner such that the parallel guidance permits a larger diameter than that corresponding to the diameter of the translation circle. The reason for this is the fact that the radial displacement of the displacer is to be limited by the rib/chamber wall combination and not by the guiding Oldham coupling. Using this rule, the dimensions of the Oldham coupling are readily determined.
It is generally believed that such Oldham couplings are not suitable for the transmission of large torques and high rpm in view of the bending fatigue exposure and frictional losses.
In all of the known Oldham couplings the lands consist of rectangular blocks engaging correspondingly shaped grooves. The objections to the use of Oldham couplings is understandable to the extent that the lateral clearance in the grooves must be minimal for uniform guidance. However, this necessarily leads to frictional surfaces which tend to wear. In addition, dirt may penetrate the coupling and jam the parts, which interferes with the operation of the coupling.